style: remove em/en dashes repo-wide, add CLAUDE.md rule against them (#890)

Em dashes (—) and en dashes (–) had spread across comments, docs, tests,
and a few UI strings, reading as AI-generated boilerplate rather than
house style. Replaced each with punctuation matching its context: colon
for explanatory clauses, comma for asides, plain hyphen for numeric/legal
ranges (e.g. "21-23§"), "to"/"till" for date ranges, parentheses for
paired-dash asides. messages/en.json and messages/sv.json were fixed by
hand together to keep sv/en in sync.

Left untouched where the dash is the functional subject rather than
decorative punctuation: date-range-parser.ts's separator regex,
charset-repair.ts's CP1252 byte-mapping table (and its test), the SIE
encoding mojibake docs, generic-csv.ts's minus-sign normalizer, the
agent system-prompt files that already instruct against em dashes, and
a golden iXBRL test fixture compared byte-for-byte.

Also fixes two bugs surfaced along the way: an off-by-one in
ApiKeysPanel's scope-label split (a leftover from an earlier partial
pass), and a charset-repair test that had lost the literal en-dash it
exists to verify.

Regenerated the agent atom seed migration (skills:generate) since 27
SKILL.md files changed. Added a CLAUDE.md rule against em/en dashes,
with an explicit carve-out for the functional-dash cases above.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

app/docs/api/reference/[slug].md/route.ts

@@ -3,17 +3,17 @@ import { buildResourcePages, RESOURCE_SLUGS } from '@/lib/docs/content/reference
 import { withPublicSecurityHeaders } from '@/lib/api/v1/security-headers'
 
 // Pre-validate the slug against the closed allow-list before any lookup
-// runs. Defense-in-depth (V1.2.5) — the lookup is array-find on a
+// runs. Defense-in-depth (V1.2.5): the lookup is array-find on a
 // memoised in-process collection so a bad slug couldn't escape into a
 // SQL or filesystem path, but the explicit allow-list gate keeps the
 // contract safe by construction if the lookup mechanism ever changes.
 const SLUG_ALLOW = new Set<string>(RESOURCE_SLUGS)
 
 // Next.js 16 does not extract the dynamic segment name from a directory
-// like `[slug].md/` — the literal `.md` suffix breaks the inference and
+// like `[slug].md/`: the literal `.md` suffix breaks the inference and
 // the framework types `params` as `{}`. Workaround: parse the slug from
 // request.url.pathname directly. Routing still works (Next.js still
-// matches /docs/api/reference/foo.md to this handler) — only the
+// matches /docs/api/reference/foo.md to this handler): only the
 // `params` typing is unusable.
 export async function GET(request: Request) {
   const url = new URL(request.url)